Meaning

noun a period of 10 years

noun the cardinal number that is the sum of nine and one; the base of the decimal system

originFrom Middle English decade, from Old French decade, from Late Latin decādem (“(set of) ten”), from Ancient Greek δεκάς (dekás), from δέκα (déka, “ten”). In reference to a span of ten years, originally a clipping of the phrase decade of years. By surface analysis, dec- + -ade. Doublet of decad and dekad.

Etymology from Wiktionary, CC BY-SA 3.0